1. Field of the Invention
This invention relates to a method for preparing organosilicon compounds that contain silicon-bonded acrylamide substituted hydrocarbon radicals. More specifically, the method involves the reaction of aminoalkylsiloxanes with acryloyl halides in nonaqueous media and in the presence of metal alkoxides to produce acylamide organosilicon compounds.
2. Background Information
Organosilicon compounds that contain silicon-bonded acylamino-substituted hydrocarbon radicals are well known and have been described in U.S. Pat. No. 4,608,270, issued Aug. 26, 1986 to Varaprath which is herein incorporated by reference.
As mentioned in Varaprath U.S. Pat. No. 4,608,270 and as taught in U.S. Pat. No. 2,929,829, issued Mar. 22, 1960, to Morehouse, Japan 56/74113, published June 19, 1981 to Takamizawa and U.S. Pat. No. 4,152,346, issued May 1, 1979, to Koetzsch et al., acylaminoorganopolysiloxanes can be synthesized by reacting aminosiloxanes with the corresponding acid chloride in the presence of a tertiary amine such as triethylamine. However, such a synthesis has several disadvantages. First, the removal of the voluminous precipitate of triethylamine hydrochloride by filtration is tedious. Second, a small amount of HCl is liberated even when an excess of amine is used. This HCl is detrimental to the stability of the polymer especially when the acid chloride has other reactive vinyl functionality such as where the acid chloride is acrylyl chloride.
An alternative method for the preparation for the acylamino organosilicon compounds involves the reaction of an acid anhydride or ester with aminosiloxanes and silanes at elevated temperature. This is taught in U.S. Pat. No. 4,507,455, issued Mar. 26, 1985, to Tangney and Ziemelis. Unfortunately at the elevated temperatures of the reaction, acrylamide derivatives undergo Michael addition and amidation of the acrylic double bond resulting in unwanted by-products and crosslinkage of the desired product which ultimately causes the polymer to gel.
Further, as taught in U.S. Pat. No. 4,608,270 to Varaprath, these problems can be overcome by reacting the aminosilanes and siloxanes with acid chlorides in the presence of aqueous sodium hydroxide. However, a problem arises from the fact that this reaction is carried out in a two-phase system in which the aminosiloxane is dissolved in an organic solvent that is immiscible with water. The HCl that is produced on addition of acyl chloride is neutralized by hydroxide in the aqueous phase. Because the amide function is generally highly polar and hydrophilic, it shows a great tendency to absorb moisture. Incorporation of these units into the siloxane backbone increases water miscibility causing the polymers to emulsify easily, thus making phase separation difficult. To some extent, this problem can be overcome by using chlorinated solvents such as methylene chloride or chloroform but, unfortunately, such solvents are toxic. Moreover, when larger amounts of amide functionality or more resinous structure or both are used, it becomes very difficult to prepare such compounds using a two-phase system even when chlorinated solvents are used. Finally, because of the presence of the aqueous phase, it is impossible to prepare aminosilanes containing hydrolytically unstable groups using this process.
Varaprath et al in U.S. Pat. No. 4,861,906, issued Aug. 29, 1989, described an improved method for preparing acylamino organosilicon compounds which avoids the phase separation and toxicity problems previously encountered. This method permits use of silane starting materials having hydrolytically unstable groups such as CH.sub.3 OSi. This method of Varaprath et al comprises reacting an acyl halide with an aminosilicon compound having at least one silicon-bonded amino-substituted hydrocarbon radical containing at least one nitrogen-bonded hydrogen in the presence of a non-aqueous solvent such as toluene or hexane, a metal alkoxide such a sodium methoxide, and a non-aqueous cosolvent for the metal alkoxide such as methanol. This reaction can be carried out at a temperature of from about -10.degree. C. to +10.degree. C. and the weight percent of methanol in a mixture of methanol and sodium methoxide can be about 1 to 25 weight percent. Varaprath et al is hereby incorporated by reference to show this process. Although this method described by Varaprath et al is an excellent method for the preparation of acylamino-organo functional organosilanes and siloxanes certain disadvantages have become apparent when the utility of these compounds are for use in the electronics industry.
Preparation of ultraviolet radiation (UV) curable compositions targeted for use on electronic devices require intermediates which will provide the desired performance. Several key criteria for such applications would include ionic purity, lot-to-lot uniformity, UV cure responsiveness, low temperature capability, thermal stability, resistance to degradation by moisture, and non-corrosivity. The Varaprath et al method is a step toward meeting these requirements, but further improvement is necessary and was thus sought.